Gestation

In 2014, NVSS introduced a new definition of the period of gestation based on the obstetric estimate of gestation at delivery, which determines the infant’s gestation in completed weeks based on the birth attendant’s final estimate of gestation. This method replaces the previous measure of gestation, which was based on the date of the last normal menses (LMP). Data on LMP gestational age are subject to error for several reasons, including imperfect maternal recall or misidentification of the last menstrual period because of postconception bleeding, delayed ovulation, or intervening early miscarriage. For more information, see: Measuring Gestational Age in Vital Statistics Data: Transitioning to the Obstetric Estimate.